Semi-conductor hearing aid amplifier



July 13, 1965 F. w. LEWIS 3,194,897

SEMI-CONDUCTOR HEARING AID AMPLIFIER Filed March 21, 1962 INVENTOR. Frazer/ex M laws CMA -IQALA- United States Patent 3,194,897 SEl'iiH-CONDUCTGR HEARING All) AREPLIFIER Frederick W. Lewis, Brooklyn Center, Minn assignor, by mesne assignments, to The Telex Corporation, Tulsa, Gida, a corporation of Delaware Filed Mar. 21, 1962, Ser. No. 181,311 6 Claims. (Cl. 179-107) This invention relates to hearing aid apparatus and is more particularly directed to apparatus for amplifying a signal falling within the audible range of frequencies.

The direction of the present state of the art in the hearing aid field is toward miniaturization of components and apparatus so as to provide greater flexibility in the placement and form of apparatus for use by the hard of hearing. A great deal of the hearing aid apparatus presently in use utilizes a means for amplifying an audio signal to compensate for discrepancies in the hearing sense organs. The present day trend toward reducing the overall size of such apparatus has seen the wide spread application of semi-conductor devices for use in amplifying audio signals along with miniaturized components for use therewith. As has been demonstrated, many of the standard components may be easily miniaturized and will provide the same function in such a state as that formally provided with much larger physical dimensions. The same is not true with the source of power necessary for energizing such apparatus. While miniaturized batteries are available, it has been found necessary to replace such batteries at an ever increasing frequency due to short life under normal operating conditions. It has been noted that the present state of the art, in utilizing a fixed power output for audio signal amplifying means results in the disadvantage of providing a most often intolerable output to the hearing sense organs of a user in the transmission of loud noises regardless of the acoustic gain of the apparatus.

The present invention provides a novel means for amplifying audio signals which makes use of resistancecapacitance coupled stages of current controlling devices which may be energized through variable impedance means from a low power source of energy to provide characteristics to be described below which overcome the above described phenomena. The application of the present invention provides a single volume control which simultaneously adjusts gain and power output, or acoustic gain and sound pressure output, so that the power output may be varied with acoustic gain to eliminate the intolerable sensation occurring upon the transmission of loud noises. In prior art applications, a low impedance source of energy has been found necessary so as to prevent the phenomenon commonly known as motor boating, or oscillation in the audio signal amplifying apparatus. The present invention utilizes a variable impedance in combination with a source of energy to simultaneously adjust the gain and output power of a high gain amplifying apparatus. As will become apparent below, the present invention provides satisfactoryoperation of amplifying apparatus which, in the general case, requires a very low energy supply impedance to prevent motor boating or oscillation in the amplifying apparatus. Further, the utilization of a series impedance in connection with the source of energy, serves to greatly extend the life of a source of energy, for instance, a mercury cell battery, since the overall gain of the amplifier is 3,l9i-,39'Z Patented July 13, 1965 ordinarily sufficient to drive a transducer at a level comfortable to the user of the hearing aid apparatus while a substantial portion of the series impedance is in circuit.

A further distinct advantage is obtained in the many applications for hearing aid apparatus in which the subject requiring a hearing aid has a low tolerance or low threshold of pain with regard to loud noises. It has been customary to vary the gain only in present day hearing aid amplifiers while maintaining the power output at a substantially constant level. Even under conditions of low gain, many of the loud noises ordinarily encountered by the user will be supplied to the auditory sense organs at a high power level resulting in discomfort to the user. By simultaneously controlling the gain and the power output, a marked improvement is obtained in this regard providing the user with substantial advantages not found in the prior art apparatus. i

It is therefore an object of the present invention to provide a hearing aid amplifier apparatus wherein a single control is provided for controlling gain and power output.

It is a further object of the present invention to provide amplifying apparatus for use in hearing aids in which a high impedance energy supply is used.

Another object of the present invention is to provide amplifying apparatus for use in a hearing aid in which the life of energy supply therefor is at a maximum.

It is a still further object of the present invention to provide a hearing aid amplifier which may be constructed of very small sized components while providing improved performance both with regard to the quality of the sound supplied to the user and the useful life of the energy supplied therefor.

These and other objects of this invention will become apparent to those skilled in the art from a consideration of the appended specification, claims and drawing in which the single figure is an electrical schematic diagram of one embodiment of my invention.

Briefly, amplifying apparatus constructed in accordance with the principles of my invention includes a source of audio signal 10, a plurality of stages of semiconductive current controlling devices of opposite conductivity type 20, 30, 40 and 5t), an output transducer 66 and a source of energy 68. V

Source of signal 10 may be a microphone having a diaphragm 11 responsive to compressional wave audio signals and an output winding 12' across which is developed an electrical signal proportional to the compressional wave energy impinging upon diaphragm 11. Output terminals 13 and 14 are provided for connection to the hearing aid amplifier apparatus. Transducer in like manner includes a coil winding 62 operative to mechanically vibrate a diaphragm 61 to generate compressional-wave energy for application to the auditory canal of the user. A pair of terminals 63 and 64 are connected to conductors 15 and 19 respectively for energization of thecur rent controlling devices comprising theamplifier apparatus. A battery source of energy 68, a variable impedance 66 having a wiper 67 and switch means are connected intermediate terminals 63 and64. l

The embodiment of the drawing includes founstages of amplification. The first stage is comprisedof'transistor 20 having emitter electrode 21, collector electrode 22 and base electrode 23. Base electrode 2.3 is connected to terminal 13 on transducer 10 through conductor 24- and capacitor 17. Emitter electrode 21 is connected to supply conductor through conductor and collector electrode 22 is connected to power supply conductor 19 through conductor 27, resistor 28, conductor 16 and resistor 38 and to base electrode 23 through conductor 27 and resistor 26. Capacitor 18 is connected intermediate con ductor 16 and supply conductor 15.

A second stage .is comprised of transistor having emitter electrode 31, collector electrode 32 and base electrode 33. Emitter electrode 31 is connected to supply conductor 19 through lead 37 and resistor 38. Collector electrode 32 is connected to power supply conductor 15 through conductor and resistor 36 and to base electrode 33 through conductor 35 and resistor 34. Base electrode 33 is connected to collector electrode 22 on transistor 20 through capacitor 29 and conductor 27.

A third stage of the amplifier apparatus is comprised of transistor having emitter electrode 41, collector electrode 42 and base electrode 43. Emitter electrode 41 is connected to supply conductor 15 through lead 54. Collector electrode 42 is connected to power supply conductor 19 through conductor 4-6 and resistor 47 and to base electrode 43 through conductor 46 and resistor 44. Base electrode 43 is connected to collector electrode 32 through capacitor 39 and-conductor 35.

The fourth and output stage of the amplifier apparatus is comprised of transistor 5i having emitter electrode 51, collector electrode 52 and base electrode 53. Emitter electrode 51 is connected to supply conductor 19 through conductor 56. Collector electrode 52 is connected to supply conductor 15 through coil winding 62 on transducer 60. Base electrode 53 is connected to collector electrode 42 on transistor 40 to capacitor 49, resistor 48 and conductor 46. Base electrode 53 is also connected to collector electrode 52 through resistor 54 having capacitor 55 connected in parallel therewith. A further capacitor 5'7 is connected intermediate supply conductors 19 and 15. For operation of the amplifier apparatus, switch 65 is closed and variable impedance 66 is adjusted to provide suitable output from transducer 60 commensurate with the requirements of the user. Sound impinging on input transducer 10 is amplified through each of the four stages and applied to the auditory canal of the user from the output of transducer 60.

The following table of values were used in constructing apparatus according to the embodiment shown in the drawing:

Reference characters: Values 10 Knowles type BE 1531 microphone. 17 1 microfarad capacitor. 18 8 microfarad capacitor. 20 Type CK 896A transistor. 26 100K ohm resistor. 28 3.3K ohm resistor. 29 1 microfarad capacitor. 30 Type CK 996A transistor. 34 100K ohm resistor. 36 3.3K ohm resistor.

38 1K ohm resistor. 39 1 microfarad capacitor. 40 Type CK 896 transistor. 44 100K ohm resistor. 47 3.3K ohm resistor. 48 10K ohm resistor. 49 1 microfarad capacitor. 50 Type CK 996 transistor. 54 68K ohm resistor. 55 .005 microfarad capacitor.

Knowles'type BC 1520 speaker. 57 8 microfarad capacitor. 66 5K ohm rheostat (audio taper). 68 Type 312 battery. 7

The illustrated embodiment was constructed of components such that the approximate size of the entire apparatus exclusive of the transducers and battery occupied a space approximately one inch long by one-eighth of an inch thick by one-quarter of an inch wide and it was found that a single cell approximately one-eighth of an inch thick and three-eighths of an inch in diameter provided satisfactory operation for use in a hearing aid in which the entire apparatus was contained in a templar member for a pair of eyeglasses of substantially the size of the common templar member utilized for eyeglass frames not incorporating hearing aid apparatus. The performance with regard to the output power and high gain was substantially improved over prior art devices in that the quality of the audio signal supplied to the auditory canal of the user was increased and the battery life was substantially extended.

It is understood that suitable modifications may be made in the structure as disclosed, provided such modifications come within the spirit and scope of the appended claims. Having now therefore fully illustrated and described my invention, what I claim to be new and desire to protect by Letters Patent is:

1. A hearing aid amplifier comprised of an even number of stages of alternately connected semi-conductive current controlling devices of opposite conductivity type; resistive and capacitive impedance means connected intermediate each of said stages; a pair of input terminals connected to the first of said stages and adapted for connection to a suitable source of audio signal; receiver means connected so as to be energized by the last of said stages for providing a compressional wave signal to the auditory canal of a user; variable impedance power supply means; and circuit means connecting 'said power supply means in energizing relationship with each of said stages whereby the gain and power output of the amplifier are simultaneously varied in accordance with the impedance of said power supply means.

2. A hearing aid amplifier for providing simultaneous adjustment of gain and power output and being of stable operation, comprising, an even number of stages of alternately connected semi-conductive current controlling devices of opposite conductivity type, resistive and capacitive impedance means connected intermediate each of said stages, a pair of input terminals connected to the first of said stages and adapted for connection to a suitable source of audio signal; receiver means connected so as to be energized by the last of said stages for providing a compressional wave signal to the auditory canal of the user; power supply means of adjustable impedance; and circuit means connecting said power supply means in energizing relationship with each of said stages, said amplifier being of variable gain and power output in response to variations in impedance of said power supply means and being stable in operation regardless of the impedance of said power supply means.

3. A hearing aid amplifier comprised of an even number of stages of alternately connected semiconductive current controlling devices of opposite conductivity type; circuit means, including series impedance means, connected intermediate each of said stages; a pair of input terminals connected to the first of said stages and adapted ,for connection to a suitable source of signal; #load means connected so as to be energized 'by the last of said stages; variable impedance power supply means; and circuit means connecting said power supply means in energizing relationship with each of said stages whereby the gain and power output of the amplifier are simultaneously varied in accordance with the impedance of said power supply means. i

4. The apparatus of claim 3 in which the series impedance means is a capacitor.

5. A hearing aid amplifier for providing simultaneous adjustment of gain and power output and being of stable operation, comprising, an even number of stages of alternately connected semi-conductive current controlling devices of opposite conductivity type, circuit means in eluding series impedance means, connected intermediate each of said stages, a pair of input terminals connected to the first of said stages and adapted for connection to a suitable source of signal; load means connected so as to be energized by the last of said stages; power supply means of adjustable impedance; and circuit means connecting said power supply means in energizing relationship with each of said stages, said amplifier being of variable gain and power output in response to variations in impedance of said power supply means and being stable in operation regardless of the impedance of said power supply means.

3 6. The apparatus of claim 5 in which the series impedance means is a capacitor.

References Cited by the Examiner UNITED STATES PATENTS ROBERT H. ROSE, Primary Examiner. 

1. A HEARING AID AMPLIFIER COMPRISED OF AN EVEN NUMBER OF STAGES OF ALTERNATELY CONNECTED SEMI-CONDUCTIVE CURRENT CONTROLLING DEVICES OF OPPOSITE CONDUCTIVITY TYPE; RESISTIVE AND CAPACITIVE IMPEDANCE MEANS CONNECTED INTERMEDIATE EACH OF SAID STAGES; A PAIR OF INPUT TERMINALS CONNECTED TO THE FIRST OF SAID STAGES AND ADAPTED FOR CONNECTION TO A SUITABLE SOURCE OF AUDIO SIGNAL; RECEIVER MEANS CONNECTED SO AS TO BE ENERGIZED BY THE LAST OF SAID STAGES FOR PROVIDING A COMPRESSIONAL WAVE SIGNAL TO THE AUDITORY CANAL OF A USER; VARIABLE IMPEDANCE POWER SUPPLY MEANS; AND CIRCUIT MEANS CONNECTING SAID POWER SUPPLY MEANS IN ENERGIZING RELATIONSHIP WITH EACH OF SAID STAGES WHEREBY THE GAIN AND POWER OUTPUT OF THE AMPLIFIER ARE SIMULTANEOUSLY VARIED IN ACCORDANCE WITH THE IMPEDANCE OF SAID POWER SUPPLY MEANS. 